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From: Martin KaFai Lau <kafai@fb.com>
To: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	David Miller <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, <kernel-team@fb.com>,
	Willem de Bruijn <willemb@google.com>
Subject: [RFC PATCH v3 net-next 1/4] net: Add skb->mono_delivery_time to distinguish mono delivery_time from (rcv) timestamp
Date: Thu, 20 Jan 2022 23:30:32 -0800	[thread overview]
Message-ID: <20220121073032.4176877-1-kafai@fb.com> (raw)
In-Reply-To: <20220121073026.4173996-1-kafai@fb.com>

skb->tstamp was first used as the (rcv) timestamp in real time clock base.
The major usage is to report it to the user (e.g. SO_TIMESTAMP).

Later, skb->tstamp is also set as the (future) delivery_time (e.g. EDT in TCP)
during egress and used by the qdisc (e.g. sch_fq) to make decision on when
the skb can be passed to the dev.

Currently, there is no way to tell skb->tstamp having the (rcv) timestamp
or the delivery_time, so it is always reset to 0 whenever forwarded
between egress and ingress.

While it makes sense to always clear the (rcv) timestamp in skb->tstamp
to avoid confusing sch_fq that expects the delivery_time, it is a
performance issue [0] to clear the delivery_time if the skb finally
egress to a fq@phy-dev.  For example, when forwarding from egress to
ingress and then finally back to egress:

            tcp-sender => veth@netns => veth@hostns => fq@eth0@hostns
                                     ^              ^
                                     reset          rest

[0] (slide 22): https://linuxplumbersconf.org/event/11/contributions/953/attachments/867/1658/LPC_2021_BPF_Datapath_Extensions.pdf

This patch adds one bit skb->mono_delivery_time to flag the skb->tstamp
is storing the mono delivery_time instead of the (rcv) timestamp.

The current use case is to keep the TCP mono delivery_time (EDT) and
to be used with sch_fq.  The later patch will also allow tc-bpf to read
and change the mono delivery_time.

In the future, another bit (e.g. skb->user_delivery_time) can be added
for the SCM_TXTIME where the clock base is tracked by sk->sk_clockid.

[ This patch is a prep work.  The following patch will
  get the other parts of the stack ready first.  Then another patch
  after that will finally set the skb->mono_delivery_time. ]

skb_set_delivery_time() function is added.  It is used by the tcp_output.c
and during ip[6] fragmentation to assign the delivery_time to
the skb->tstamp and also set the skb->mono_delivery_time.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
---
 include/linux/skbuff.h                     | 13 +++++++++++++
 net/bridge/netfilter/nf_conntrack_bridge.c |  5 +++--
 net/ipv4/ip_output.c                       |  5 +++--
 net/ipv4/tcp_output.c                      | 16 +++++++++-------
 net/ipv6/ip6_output.c                      |  5 +++--
 net/ipv6/netfilter.c                       |  5 +++--
 6 files changed, 34 insertions(+), 15 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index bf11e1fbd69b..b9e20187242a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -720,6 +720,10 @@ typedef unsigned char *sk_buff_data_t;
  *	@dst_pending_confirm: need to confirm neighbour
  *	@decrypted: Decrypted SKB
  *	@slow_gro: state present at GRO time, slower prepare step required
+ *	@mono_delivery_time: When set, skb->tstamap has the
+ *		delivery_time in mono clock base (i.e. EDT).  Otherwise, the
+ *		skb->tstamp has the (rcv) timestamp at ingress and
+ *		delivery_time at egress.
  *	@napi_id: id of the NAPI struct this skb came from
  *	@sender_cpu: (aka @napi_id) source CPU in XPS
  *	@secmark: security marking
@@ -890,6 +894,7 @@ struct sk_buff {
 	__u8			decrypted:1;
 #endif
 	__u8			slow_gro:1;
+	__u8			mono_delivery_time:1;
 
 #ifdef CONFIG_NET_SCHED
 	__u16			tc_index;	/* traffic control index */
@@ -3903,6 +3908,14 @@ static inline ktime_t net_invalid_timestamp(void)
 	return 0;
 }
 
+static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
+					 bool mono)
+{
+	skb->tstamp = kt;
+	/* Setting mono_delivery_time will be enabled later */
+	/* skb->mono_delivery_time = kt && mono; */
+}
+
 static inline u8 skb_metadata_len(const struct sk_buff *skb)
 {
 	return skb_shinfo(skb)->meta_len;
diff --git a/net/bridge/netfilter/nf_conntrack_bridge.c b/net/bridge/netfilter/nf_conntrack_bridge.c
index fdbed3158555..ebfb2a5c59e4 100644
--- a/net/bridge/netfilter/nf_conntrack_bridge.c
+++ b/net/bridge/netfilter/nf_conntrack_bridge.c
@@ -32,6 +32,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk,
 					   struct sk_buff *))
 {
 	int frag_max_size = BR_INPUT_SKB_CB(skb)->frag_max_size;
+	bool mono_delivery_time = skb->mono_delivery_time;
 	unsigned int hlen, ll_rs, mtu;
 	ktime_t tstamp = skb->tstamp;
 	struct ip_frag_state state;
@@ -81,7 +82,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk,
 			if (iter.frag)
 				ip_fraglist_prepare(skb, &iter);
 
-			skb->tstamp = tstamp;
+			skb_set_delivery_time(skb, tstamp, mono_delivery_time);
 			err = output(net, sk, data, skb);
 			if (err || !iter.frag)
 				break;
@@ -112,7 +113,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk,
 			goto blackhole;
 		}
 
-		skb2->tstamp = tstamp;
+		skb_set_delivery_time(skb2, tstamp, mono_delivery_time);
 		err = output(net, sk, data, skb2);
 		if (err)
 			goto blackhole;
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 57c1d8431386..6ba08d9bdf8e 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -754,6 +754,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 {
 	struct iphdr *iph;
 	struct sk_buff *skb2;
+	bool mono_delivery_time = skb->mono_delivery_time;
 	struct rtable *rt = skb_rtable(skb);
 	unsigned int mtu, hlen, ll_rs;
 	struct ip_fraglist_iter iter;
@@ -836,7 +837,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 				ip_fraglist_prepare(skb, &iter);
 			}
 
-			skb->tstamp = tstamp;
+			skb_set_delivery_time(skb, tstamp, mono_delivery_time);
 			err = output(net, sk, skb);
 
 			if (!err)
@@ -892,7 +893,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		/*
 		 *	Put this fragment into the sending queue.
 		 */
-		skb2->tstamp = tstamp;
+		skb_set_delivery_time(skb2, tstamp, mono_delivery_time);
 		err = output(net, sk, skb2);
 		if (err)
 			goto fail;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 5079832af5c1..261e9584f81e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1253,7 +1253,7 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
 	tp = tcp_sk(sk);
 	prior_wstamp = tp->tcp_wstamp_ns;
 	tp->tcp_wstamp_ns = max(tp->tcp_wstamp_ns, tp->tcp_clock_cache);
-	skb->skb_mstamp_ns = tp->tcp_wstamp_ns;
+	skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);
 	if (clone_it) {
 		oskb = skb;
 
@@ -1589,7 +1589,7 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
 
 	skb_split(skb, buff, len);
 
-	buff->tstamp = skb->tstamp;
+	skb_set_delivery_time(buff, skb->tstamp, true);
 	tcp_fragment_tstamp(skb, buff);
 
 	old_factor = tcp_skb_pcount(skb);
@@ -2616,7 +2616,8 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 
 		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
 			/* "skb_mstamp_ns" is used as a start point for the retransmit timer */
-			skb->skb_mstamp_ns = tp->tcp_wstamp_ns = tp->tcp_clock_cache;
+			tp->tcp_wstamp_ns = tp->tcp_clock_cache;
+			skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);
 			list_move_tail(&skb->tcp_tsorted_anchor, &tp->tsorted_sent_queue);
 			tcp_init_tso_segs(skb, mss_now);
 			goto repair; /* Skip network transmission */
@@ -3541,11 +3542,12 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 	now = tcp_clock_ns();
 #ifdef CONFIG_SYN_COOKIES
 	if (unlikely(synack_type == TCP_SYNACK_COOKIE && ireq->tstamp_ok))
-		skb->skb_mstamp_ns = cookie_init_timestamp(req, now);
+		skb_set_delivery_time(skb, cookie_init_timestamp(req, now),
+				      true);
 	else
 #endif
 	{
-		skb->skb_mstamp_ns = now;
+		skb_set_delivery_time(skb, now, true);
 		if (!tcp_rsk(req)->snt_synack) /* Timestamp first SYNACK */
 			tcp_rsk(req)->snt_synack = tcp_skb_timestamp_us(skb);
 	}
@@ -3594,7 +3596,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 	bpf_skops_write_hdr_opt((struct sock *)sk, skb, req, syn_skb,
 				synack_type, &opts);
 
-	skb->skb_mstamp_ns = now;
+	skb_set_delivery_time(skb, now, true);
 	tcp_add_tx_delay(skb, tp);
 
 	return skb;
@@ -3771,7 +3773,7 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
 
 	err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
 
-	syn->skb_mstamp_ns = syn_data->skb_mstamp_ns;
+	skb_set_delivery_time(syn, syn_data->skb_mstamp_ns, true);
 
 	/* Now full SYN+DATA was cloned and sent (or not),
 	 * remove the SYN from the original skb (syn_data)
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 2995f8d89e7e..4b873413edc2 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -813,6 +813,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 	struct rt6_info *rt = (struct rt6_info *)skb_dst(skb);
 	struct ipv6_pinfo *np = skb->sk && !dev_recursion_level() ?
 				inet6_sk(skb->sk) : NULL;
+	bool mono_delivery_time = skb->mono_delivery_time;
 	struct ip6_frag_state state;
 	unsigned int mtu, hlen, nexthdr_offset;
 	ktime_t tstamp = skb->tstamp;
@@ -903,7 +904,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 			if (iter.frag)
 				ip6_fraglist_prepare(skb, &iter);
 
-			skb->tstamp = tstamp;
+			skb_set_delivery_time(skb, tstamp, mono_delivery_time);
 			err = output(net, sk, skb);
 			if (!err)
 				IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
@@ -962,7 +963,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		/*
 		 *	Put this fragment into the sending queue.
 		 */
-		frag->tstamp = tstamp;
+		skb_set_delivery_time(frag, tstamp, mono_delivery_time);
 		err = output(net, sk, frag);
 		if (err)
 			goto fail;
diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
index 6ab710b5a1a8..1da332450d98 100644
--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -121,6 +121,7 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 				  struct sk_buff *))
 {
 	int frag_max_size = BR_INPUT_SKB_CB(skb)->frag_max_size;
+	bool mono_delivery_time = skb->mono_delivery_time;
 	ktime_t tstamp = skb->tstamp;
 	struct ip6_frag_state state;
 	u8 *prevhdr, nexthdr = 0;
@@ -186,7 +187,7 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 			if (iter.frag)
 				ip6_fraglist_prepare(skb, &iter);
 
-			skb->tstamp = tstamp;
+			skb_set_delivery_time(skb, tstamp, mono_delivery_time);
 			err = output(net, sk, data, skb);
 			if (err || !iter.frag)
 				break;
@@ -219,7 +220,7 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 			goto blackhole;
 		}
 
-		skb2->tstamp = tstamp;
+		skb_set_delivery_time(skb2, tstamp, mono_delivery_time);
 		err = output(net, sk, data, skb2);
 		if (err)
 			goto blackhole;
-- 
2.30.2


  reply	other threads:[~2022-01-21  7:30 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-21  7:30 [RFC PATCH v3 net-next 0/4] Preserve mono delivery time (EDT) in skb->tstamp Martin KaFai Lau
2022-01-21  7:30 ` Martin KaFai Lau [this message]
2022-01-22 15:32   ` [RFC PATCH v3 net-next 1/4] net: Add skb->mono_delivery_time to distinguish mono delivery_time from (rcv) timestamp Willem de Bruijn
2022-01-22 19:52     ` Martin KaFai Lau
2022-01-22 20:03     ` Martin KaFai Lau
2022-01-21  7:30 ` [RFC PATCH v3 net-next 2/4] net: Add skb_clear_tstamp() to keep the mono delivery_time Martin KaFai Lau
2022-01-21  7:30 ` [RFC PATCH v3 net-next 3/4] net: Set skb->mono_delivery_time and clear it when delivering locally Martin KaFai Lau
2022-01-21 12:02   ` Julian Anastasov
2022-01-22  3:28     ` Martin KaFai Lau
2022-01-21  7:30 ` [RFC PATCH v3 net-next 4/4] bpf: Add __sk_buff->mono_delivery_time and handle __sk_buff->tstamp based on tc_at_ingress Martin KaFai Lau
2022-01-21 18:50   ` sdf
2022-01-21 20:56     ` Martin KaFai Lau
2022-01-21 22:33       ` sdf
2022-01-22 15:43 ` [RFC PATCH v3 net-next 0/4] Preserve mono delivery time (EDT) in skb->tstamp Willem de Bruijn
2022-01-22 21:05   ` Martin KaFai Lau

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